1. Field of Invention
This invention relates to electronic circuitry for generating a signal coincident with a selected cylinder ignition signal in an engine.
2. Description of the Prior Art
A number of diagnostic procedures relating to electric ignition internal combustion engines are dependent on identification of the timing of a selected cylinder, such as the ignition of the number one cylinder. It has been common simply to utilize the high voltage tapped off the number one cylinder ignition cable as a trigger or strobe pulse for operation of other apparatus, such as a timing light. However, in complex electronic engine analysis apparatus, the exact timing of the signal and the assurance that the detected signal is in fact the number one ignition signal, rather than a spurious noise signal of some sort, all become more important.
Although it is possible to use filtering techniques to filter out noise and to pass only signals at a given frequency whenever the signals are fixed in frequency, such techniques are not of any value at all where a signal, such as an ignition signal, although repetitive and cyclic in nature, has a randomly varying repetition rate or frequency.